As an example of cutting inserts for use in the threading process, an indexable insert (cutting insert) described in Patent Document 1 has conventionally been known. The cutting insert described in Patent Document 1 includes a cutting edge located at a corner part of a major surface, a rake surface which is located along the cutting edge and has a protrusion disposed on the rake surface, and a saw tooth-shaped inclined surface located behind the rake surface. The inclined surface is inclined relative to a bisector of the cutting edge as a whole in a top view.
With a machining method, which is called radial infeed in the threading process, a chip flow is apt to be unstable. However, the above-mentioned inclined surface makes it easy to control a chip flow direction.
In the cutting insert described in Patent Document 1, the inclined surface is located behind the protrusion. Therefore, because a distance from the cutting edge to the inclined surface is long, the chip flow direction may become unstable before chips come into contact with the inclined surface. Thus, even with the cutting insert described in Patent Document 1, the control of the chip flow is not enough, and it may be difficult to control the chip flow direction through the inclined surface.